'In a sense I have always felt something of a kinship with the coloured race because its position is the same as mine," says Ignatius J Reilly, the hopeless protagonist of John Kennedy Toole's A Confederacy of Dunces. "We both exist outside the inner realm of American society. Of course, my exile is voluntary. However, it is apparent that many of the Negroes wish to become active members of the American middle class. I cannot imagine why. I must admit that this desire on their part leads me to question their value judgments. However if they wish to join the bourgeoisie, it is really none of my business. They may seal their own doom."

As any neocon will tell you, there is nothing quite so frustrating as trying to liberate people who just do not appreciate the freedom you have in store for them. Nor is there much joy in expressing solidarity with people who want nothing to do with you. The "historic" alliances that have been announced between workers, peasants, students, women and gays would indeed have changed history. Sadly, the vast majority were never truly forged.

Nowhere does this contradiction seem more acute than in the fortunes of the Democratic party, which has stood with the professed aim of representing the economic interests of poorer Americans over the past 40 years.

According to recent US census figures, since President Bush assumed power in 2000 poverty has risen by 7%, the proportion of those without healthcare has risen by 9%, and median household income has fallen by 3%. But where the poor are most numerous, it seems the Democrats are weakest. The 10 states with the lowest household median income, where people are least likely to have healthcare and most likely to live in poverty, all voted Republican in 2004. Not only are they poor, but they're getting poorer. The five states with the steepest falls in income backed Bush.

Indeed, if anything the Democrats' base seems to be among the wealthy. The same census figures showed that seven of the 10 states with the highest median incomes voted Democrat, and citizens who lived in Democrat states were less likely to live in poverty and more likely to have health insurance. And these states are getting wealthier. The five with the sharpest increase in income all voted Democrat in 2004.

Bill Clinton won in 1992 with the dictum "It's the economy, stupid". But what to make of a political culture where poor states elect the party that represents the interests of the rich and vice versa?

This is not a new question but a perennially pertinent one, because it has shaped an understanding of US politics since the late 60s. It underpins the assumptions that send Bush clearing brush for the cameras and the reason why accusations that Kerry "looked French" resonate.

In his book What's The Matter With Kansas?, Thomas Frank described the tendency of working-class people to vote Republican as a form of derangement. He said that the working class had been hoodwinked into voting against its economic interests by "values" issues such as abortion and gay rights.

There were two main problems with this argument. First, it suggested that poor people are incapable of working out what's best for them. Second, it gave undue emphasis to economic interests, as if they should always take primacy at the ballot box. My guess is that Frank, along with many readers of this paper, vote against their economic interests when they vote for a government that will raise taxes and redistribute wealth. It doesn't follow that, because poor people also put different priorities (opposing gay marriage or abortion) with which we disagree ahead of financial wellbeing, we are principled and they are patsies.

But there was, as it turned out, another flaw with Frank's book. The central premise on which it was written was debatable, if not debunkable. Last year Larry Bartels, a professor of politics and public affairs at Princeton, wrote a paper called: What's The Matter With What's The Matter With Kansas?. (It is a testament to the influence of Frank's work that those who seek to subvert its message must first subvert its title.)

The white working class, insisted Bartels, hadn't abandoned the Democratic party, and neither their moral values nor their religion distracted them from their economic interests. Bartels's argument was not quite as devastating as he claimed (Frank's facts stand up if you assess class by educational attainment rather than income), but it undermined the key assumption that poor white people vote Republican. They don't. According to CNN polls, 63% per cent of those who earn less than $15,000 a year and 57% of those who earn between $15,000 and $30,000 voted Democrat. The poorer you are, the more likely you are to vote Democrat.

So how are we to understand the fact that the poorest states voted for Bush? Soon after Bartels's paper came another by four academics, subtitled: Rich State, Poor State, Red State, Blue State, What's The Matter With Connecticut?. It revealed that rich people in poor states are more motivated to vote Republican, whereas in wealthier states there is a lower correlation between income and voting preference. In other words, thinking of the American political landscape in terms of different states (remember the map with the Democrat blue on the edges flanking a sea of Republican red?) hides the often far more important differences within states.

So what's the matter with all these analyses? First of all they seem to step over a huge elephant in the room - namely race. There is a reason why we are only talking about white working-class voters: black people, regardless of income, overwhelmingly vote Democrat. Indeed, were it not for black people, the Democrats would have won the presidency only once, in 1964. That was the year President Lyndon Johnson signed the civil rights act, turned to an aide and said: "We have lost the south for a generation." We are well into the second generation now, and the racialised politics of the south seem to be influencing the rest of the country rather than the other way round.

In other words there is a clear racial attachment that white voters have to the Republican party that does not override income but certainly qualifies it. No understanding of why so many of them vote Republican can examine class as though it is distinct from race.

Second, they assume a greater class attachment to the Democrats than the party deserves. Unlike the Republicans, who openly lobby for the class interests of their supporters and deliver on them, Democrats do not promise substantial changes to the lives of ordinary working people in America and rarely deliver even on the symbolic ones.

Which brings us to the final problem. The strongest correlation between income and voting is not whom you vote for but if you vote at all. The more you earn, the more likely you are to turn out. According to the census, 81.3% of those who earned $100,000 or more turned out in 2004; the figure for those who earned less than $20,000 was 48%.

That's because the rich have something to vote for. They have two parties; the poor here have none. Ultimately, the question of what's the matter with Kansas or any other state must in no small part be answered by yet another one: what's the matter with Democrats?